Before air conditioners, people would keep things cool with big blocks of ice. When air conditioners were introduced, their output ratings were judged based on how much ice you would need to get the same cooling power.
The first air conditioner was invented by Willis Carrier in 1902. He worked at a publishing company and needed a way to keep his paper from expanding and ink from running.
Herbert Hoover was the first President to enjoy the air conditioning. He spent $30,000 to install the system in the oval office, just after the start of the Great Depression